Illumination unit and display

ABSTRACT

An illumination unit includes: a light source section including a laser light source; an optical-path branching device outputting light incident from the light source section, by branching the light into an outgoing optical path of illumination light and other optical path; a photodetector receiving a light flux that travels on the other optical path; a control section controlling an emitted light quantity in the laser light source, based on a quantity of the light flux received by the photodetector; and a light-quantity-distribution control device disposed between the optical-path branching device and the photodetector on the other optical path, the light-quantity-distribution control device controlling a light quantity distribution in the light flux to be incident upon the photodetector.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/407,853, filed on Jan. 17, 2017, which is a continuation ofU.S. patent application Ser. No. 15/050,322, filed Feb. 22, 2016 (nowU.S. Pat. No. 9,584,779), which is a continuation of U.S. patentapplication Ser. No. 13/540,740, filed on Jul. 3, 2012 (now U.S. Pat.No. 9,285,101), which claims priority from Japanese patent application2011-153485 filed on Jul. 12, 2011. Each of the above applications areincorporated herein by reference in their entirety.

BACKGROUND

The disclosure relates to an illumination unit that emits lightincluding a laser beam, and a display that displays an image by usingsuch an illumination unit.

In general, an optical module, which is one of main parts of a projector(a projection-type display), is configured to have an illuminationoptical system (an illumination unit) and a projection optical system.The illumination optical system includes a light source, and theprojection optical system includes a light modulation device. In thefield of such a projector, small (palmtop) and lightweight portableprojectors called “micro-projector” have become widespread in recentyears. In this micro-projector, LED (Light Emitting Diode) has beenmainly used as the light source of the illumination unit.

Meanwhile, lately, lasers have been receiving attention as a new type oflight source for the illumination unit. For instance, following thecommercialization of high-output blue semiconductor lasers and redsemiconductor lasers, development of green semiconductor lasers has beenunderway and is about to reach a practical level. Against this backdrop,there has been suggested a projector in which single-color lasers(semiconductor lasers) for three primary colors of red (R), green (G),and blue (B) are used as a light source of the illumination unit. Use ofthe single-color laser as the light source makes it possible to obtain aprojector in which a color reproduction range is wide and powerconsumption is low.

Further, in recent years, there has been a demand for improvements insize (downsizing) and brightness of portable projectors. This isbecause, in existing small semiconductor lasers, although output isconsidered to be high, brightness tends to be insufficient. Therefore,development of semiconductor lasers with higher output has beenvigorously pursued.

SUMMARY

Among the projectors using the laser as the light source as describedabove, a projector that monitors a part of illumination light by using aphotodetector (a light sensing device) has been suggested (for example,see Japanese Unexamined Patent Application Publication No. 2001-343703).As for the semiconductor laser, for instance, a characteristic usuallychanges depending on a temperature change, aging degradation, and thelike. Therefore, it is necessary to correct a current fed into thesemiconductor laser, so as to achieve desired display luminance(brightness). For this reason, in one of techniques for such correction,a photodetector is disposed in an optical system of the projector, and apart of a laser beam (illumination light) is monitored to detect a lightquantity, and thereby an emitted light quantity is controlled to be keptconstant.

However, when the part of the outgoing beam (the illumination light)from the laser light source is monitored as described above, it is noteasy to respond to a temperature change in the light quantitydistribution in some cases, making it difficult to perform accuratelight control. Therefore, there is desired suggestion of a techniquethat reduces variations in the quantity of the illumination light, whichare caused by the temperature changes in the light quantity distributionof the laser beam, when the part of the illumination light from thelaser serving as the light source is monitored.

It is desirable to provide an illumination unit and a display which arecapable of reducing variations in the quantity of illumination light.

According to an embodiment of the disclosure, there is provided anillumination unit including: a light source section including a laserlight source; an optical-path branching device outputting light incidentfrom the light source section, by branching the light into an outgoingoptical path of illumination light and other optical path; aphotodetector receiving a light flux that travels on the other opticalpath; a control section controlling an emitted light quantity in thelaser light source, based on a quantity of the light flux received bythe photodetector; and a light-quantity-distribution control devicedisposed between the optical-path branching device and the photodetectoron the other optical path, the light-quantity-distribution controldevice controlling a light quantity distribution in the light flux to beincident upon the photodetector.

According to an embodiment of the disclosure, there is provided adisplay including an illumination unit that emits illumination light,and a light modulation device that modulates the illumination lightbased on an image signal. The illumination unit includes: a light sourcesection including a laser light source; an optical-path branching deviceoutputting light incident from the light source section, by branchingthe light into an outgoing optical path of illumination light and otheroptical path; a photodetector receiving a light flux traveling on theother optical path; a control section controlling an emitted lightquantity in the laser light source, based on a quantity of the lightflux received by the photodetector; and a light-quantity-distributioncontrol device disposed between the optical-path branching device andthe photodetector on the other optical path, thelight-quantity-distribution control device controlling a light quantitydistribution in the light flux to be incident upon the photodetector.

In the illumination unit and the display according to theabove-described embodiments of the disclosure, the light incident fromthe light source section upon the optical-path branching device isbranched into the outgoing optical path of the illumination light andthe other optical path, and the branched light is outputted. The lightflux traveling on the other optical path is received by thephotodetector, and the emitted light quantity in the laser light sourceis controlled based on the quantity of this received light flux. Here,the light quantity distribution in the light flux to be incident uponthe photodetector is controlled by the light-quantity-distributioncontrol device disposed between the optical-path branching device andthe photodetector on the other optical path. This makes the lightquantity distribution in the light flux incident upon the photodetectorbecome less likely to vary, even when the light quantity distribution inthe laser beam emitted from the laser light source changes depending onthe temperature. Thus, accuracy of controlling the emitted lightquantity in the laser light source improves.

According to the illumination unit and the display in theabove-described embodiments of the technology, thelight-quantity-distribution control device is provided between theoptical-path branching device and the photodetector on the other opticalpath different from the outgoing optical path of the illumination light.The light-quantity-distribution control device controls the lightquantity distribution in the light flux to be incident upon thephotodetector. Therefore, in a case where a temperature change occurs inthe light quantity distribution of the laser beam, the accuracy ofcontrolling the emitted light quantity in the laser light source isenhanced. Hence, light-quantity variations in the illumination light arereduced.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the technology as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate embodiments and,together with the specification, serve to explain the principles of thetechnology.

FIG. 1 is a diagram illustrating an overall configuration of a displayaccording to a first embodiment of the disclosure.

FIGS. 2A and 2B are diagrams illustrating an example of an ideal lightquantity distribution in a laser beam.

FIGS. 3A and 3B are diagrams illustrating an example of an actual lightquantity distribution in a laser beam.

FIG. 4 is a diagram illustrating an overall configuration of a displayaccording to a comparative example.

FIG. 5 is a schematic diagram illustrating an example of a relationshipbetween a light-receiving surface of a photodetector and an incidentlight flux depicted in FIG. 4.

FIGS. 6A and 6B are diagrams illustrating an example of a light quantitydistribution of the incident light flux depicted in FIG. 5.

FIGS. 7A to 7C are diagrams each illustrating an example of temperaturecharacteristics in the light quantity distribution of the incident lightflux depicted in FIG. 6.

FIGS. 8A and 8B are diagrams illustrating an optical path example ofeach light beam in the light flux incident upon the photodetectoraccording to the comparative example, and that according to Example 1,respectively.

FIGS. 9A and 9B are diagrams illustrating an example of the lightquantity distribution of the light flux incident upon the photodetectoraccording to the comparative example, and that according to Example 1,respectively.

FIG. 10 is a diagram illustrating an overall configuration of a displayaccording to a second embodiment.

FIGS. 11A and 11B are diagrams illustrating an optical path example ofeach light beam in the light flux incident upon the photodetector, andan example of the light quantity distribution of the light flux incidentupon the photodetector, respectively, according to Example 2.

FIGS. 12A and 12B are diagrams illustrating an optical path example ofside lobe light in the light flux incident upon the photodetectoraccording to the comparative example, and that according to Example 2,respectively.

FIGS. 13A and 13B are diagrams illustrating an example of the lightquantity distribution of the side lobe light on the photodetectoraccording to the comparative example, and that according to Example 2,respectively.

FIG. 14 is a diagram illustrating an overall configuration of a displayaccording to a third embodiment.

FIGS. 15A and 15B are diagrams illustrating an example of the lightquantity distribution in a P-polarized light component of a laser beam,and that in an S-polarized light component of the laser beam,respectively.

FIG. 16 is a diagram illustrating an example of the light quantity foreach polarized component in each of the illumination light and the light(incident light flux) traveling to the photodetector.

FIG. 17 is a diagram illustrating an example of a temperature change inthe light quantity for each polarized component in light emitted from alaser.

FIG. 18 is a diagram illustrating an overall configuration of a displayaccording to a fourth embodiment.

FIG. 19 is a diagram illustrating an example of reflection andtransmission characteristics for each polarized component in areflection transmission film depicted in FIG. 18.

FIG. 20 is a diagram illustrating an overall configuration of a displayaccording to a fifth embodiment.

FIGS. 21(A), 21(B), 21(C) and 21(D) are diagrams illustrating a lightquantity for each polarized component in each of the illumination lightand the light traveling to the photodetector, according to Example 3.

FIGS. 22(A), 22(B), 22(C) and 22(D) are diagrams illustratingtemperature characteristics of the light quantity in each of theillumination light and the light traveling to the photodetector,according to Example 3.

FIGS. 23(A), 23(B) and 23(C) are diagrams illustrating a temperaturechange rate of the light quantity in each of the illumination light andthe light traveling to the photodetector, according to Example 3.

FIG. 24 is a characteristic diagram illustrating a relationship betweenthe temperature change rate of the light quantity and a reflectance forthe P-polarized light component in a dichroic prism, according toExample 3.

DETAILED DESCRIPTION

Embodiments of the disclosure will be described below in detail withreference to the drawings. It is to be noted that the description willbe provided in the following order.

1. First embodiment (an example in which a coupling lens is used as alight-quantity-distribution control device)

2. Second embodiment (an example in which a diffusion device is used asa light-quantity-distribution control device)

3. Third embodiment (an example in which a polarizing device controllingpolarized components of light traveling to a photodetector is provided)

4. Fourth embodiment (an example 1 in which characteristics of areflection transmission film of a dichroic prism is adjusted)

5. Fifth embodiment (an example 2 in which characteristics of areflection transmission film of a dichroic prism is adjusted)

6. Modifications

First Embodiment [Configuration of Display 3]

FIG. 1 illustrates an overall configuration of a display (a display 3)according to a first embodiment of the disclosure. The display 3 is aprojection-type display that projects an image (image light) onto ascreen 30 (a projection surface). The display 3 includes an illuminationunit 1, and an optical system (a display optical system) provided toperform image display by using illumination light from the illuminationunit 1.

(Illumination Unit 1)

The illumination unit 1 includes a red laser 11R, a green laser 11G, ablue laser 11B, coupling lenses 12R, 12G, and 12B, dichroic prisms 131and 132, an optical device 14, a collimator lens 151, a fly-eye lens152, and a condensing lens 153. The illumination unit 1 further includesa coupling lens 12, a photodetector (a light sensing device) 17, and acontrol section 18. It is to be noted that Z0 in FIG. 1 indicates anoptical axis.

The red laser 11R, the green laser 11G, and the blue laser 11B are threekinds of light sources emitting a red laser beam, a green laser beam, ablue laser beam, respectively. These light sources form a light sourcesection, and here, each of these three kinds of light sources is a laserlight source. The red laser 11R, the green laser 11G, and the blue laser11B each perform pulse emission, for example. In other words, each ofthe red laser 11R, the green laser 11G, and the blue laser 11B outputs alaser beam intermittently, at a predetermined emission frequency (anemission period), for example. Each of the red laser 11R, the greenlaser 11G, and the blue laser 11B is, for instance, a semiconductorlaser, a solid-state laser, or the like. It is to be noted that wheneach of these laser light sources is the semiconductor laser, forinstance, a wavelength λr of the red laser beam is about 600 to about700 nm, a wavelength λg of the green laser beam is about 500 to about600 nm, and a wavelength λb of the blue laser beam is about 400 to about500 nm.

The coupling lenses 12G and 12B are provided to collimate the greenlaser beam emitted from the green laser 11G and the blue laser beamemitted from the blue laser 11B (to release these laser beams asparallel beams), and couple the collimated beams to the dichroic prism131. Similarly, the coupling lens 12R is provided to collimate the redlaser beam emitted from the red laser 11R (to release this laser beam asa parallel beam), and couple the collimated beam to the dichroic prism132. It to be noted that, here, the laser beams being incident are eachcollimated (to serve as the parallel beam) by the coupling lenses 12R,12G, and 12B, but are not limited to this example, and may not becollimated (may not become the parallel beams) by the coupling lenses12R, 12G, and 12B. Nevertheless, collimating the laser beams asdescribed above leads to a reduction in size of the unit configurationand thus is more preferable.

The dichroic prism 131 selectively reflects the green laser beamentering through the coupling lens 12G, while selectively allowing theblue laser beam entering through the coupling lens 12B to passtherethrough. The dichroic prism 132 selectively reflects the red laserbeam entering through the coupling lens 12R, while selectively allowingthe blue laser beam and the green laser beam outputted from the dichroicprism 131 to pass therethrough. This realizes color composition (opticalpath synthesis) of the red laser beam, the green laser beam, and theblue laser beam.

The dichroic prism 132 also functions as an optical-path branchingdevice. This optical-path branching device branches the laser beams ofthe respective colors incident from the red laser 11R, the green laser11G, and the blue laser 11B, into an outgoing optical path L1 of theillumination light and a light-receiving optical path L2 (other opticalpath) to the photodetector 17 which will be described later. Theoptical-path branching device then outputs the branched laser beams.Such a function of serving as the optical-path branching device isrealized by a reflection transmission film 130 disposed on adhesionsurfaces of a pair of prisms therebetween. The reflection transmissionfilm 130 is configured by forming a multilayer film in which dielectricmaterials having different refractive indexes such as titanium oxide(TiO₂) and silicon oxide (SiO₂) are laminated, for example. Themultilayer film is formed like a mirror surface. The reflectiontransmission film 130 provides an optical reflectance and an opticaltransmittance with respect to the incident light. It is to be noted thatsince the optical reflectance in this dichroic prism 132 is about a fewpercent which is low, most of the light travels on the outgoing opticalpath L1 and is used as the illumination light.

The optical device 14 is disposed on an optical path between the lightsource and the fly-eye lens 152 (specifically, between the dichroicprism 132 and the collimator lens 151 on the outgoing optical path L1).The optical device 14 is provided to reduce a so-called speckle noise(an interference pattern). The laser beam traveling on the outgoingoptical path L1 passes through this optical device 14. Specifically, theoptical device 14 is caused to vibrate (to perform micro vibration) by adrive section which is not illustrated (for example, the optical device14 is caused to vibrate in a direction along the optical axis Z0 or adirection orthogonal to the optical axis Z0), and thereby the specklenoise is reduced.

The collimator lens 151 is disposed between the optical device 14 andthe fly-eye lens 152 on the outgoing optical path L1, and collimates thelight outputted from the optical device 14 to release the light as aparallel beam.

The fly-eye lens 152 is an optical member (an integrator) in which aplurality of lenses are arranged two-dimensionally on a substrate, andoutputs an incident light flux after spatially dividing this light fluxaccording to an arrangement of these lenses. Thus, the light outputtedfrom this fly-eye lens 152 is made uniform (an in-plane intensitydistribution is made uniform), and outputted as the illumination light.

The condensing lens 153 is provided to condense the incident light (theillumination light) which has been made uniform by the fly-eye lens 152.

The coupling lens 12 is disposed between the dichroic prism 132 and thephotodetector 17 on the light-receiving optical path L2, and functionsas a refractive device with positive power. This allows the couplinglens 12 to control a light quantity distribution in a light flux to beincident upon the photodetector 17, as will be described later indetail. This coupling lens 12 corresponds to a specific but notlimitative example of “light-quantity-distribution control device” inthe disclosure.

The photodetector 17 is a device receiving the light flux travelingalong the light-receiving optical path L2, on a light-receiving surface170, and functions as a light quantity detector that detects (monitors)the quantity of the light flux. The photodetector 17 includes thelight-receiving surface 170. The light-receiving surface 17 issufficiently smaller than a cross-sectional area of the light flux(i.e., a beam area) traveling on the light-receiving optical path L2, soas to prevent detection of excess light including stray light on theoptical path and light reflected from a reflection-type liquid crystaldevice 21, as will be described later.

The control section 18 controls an emitted light quantity in the redlaser 11R, the green laser 11G, and the blue laser 11B, based on thequantity of the light flux received by the photodetector 17 (i.e. thecontrol section 18 serves as an automatic power controller).Specifically, the control section 18 controls the emitted light quantityin the red laser 11R, the green laser 11G, and the blue laser 11B, sothat the emitted light quantity becomes substantially constant(desirably, constant), without depending on a temperature change. Here,specifically, for instance, the control section 18 feeds the detectedlight quantity back to each of the red laser 11R, the green laser 11G,and the blue laser 11B, and then controls the voltage of each of thelaser light sources after performing I-V (current-voltage) conversion.

(Display Optical System)

The display optical system mentioned above is configured using apolarization beam splitter (PBS) 23, a field lens 22, thereflection-type liquid crystal device 21, and a projection lens 24 (aprojection optical system).

The polarization beam splitter 23 is an optical member that selectivelyallows specific polarized light (e.g., P-polarized light) to passtherethrough, while selectively reflecting other polarized light (e.g.,S-polarized light). Thus, the illumination light (e.g., the S-polarizedlight) from the illumination unit 1 is selectively reflected andincident upon the reflection-type liquid crystal device 21, while theimage light (e.g., the P-polarized light) outputted from this reflectingliquid crystal device 21 selectively passes through the polarizationbeam splitter 23 and is then incident upon the projection lens 24.

The field lens 22 is disposed on an optical path between thepolarization beam splitter 23 and the reflection-type liquid crystaldevice 21. The field lens 22 is provided to reduce the size of theoptical system, by causing tencentric incidence of the illuminationlight upon the reflection-type liquid crystal device 21.

The reflection-type liquid crystal device 21 is a light modulationdevice that outputs the image light, by reflecting the illuminationlight from the illumination unit 1 while modulating this illuminationlight based on an image signal supplied from the display control sectionwhich is not illustrated. Here, in the reflection-type liquid crystaldevice 21, the illumination light is reflected so that the polarizedlight (e.g., the S-polarized light or the P-polarized light) whenincident and that when outputted are different from each other. Thisreflection-type liquid crystal device 21 is, for example, a liquidcrystal device such as LCOS (Liquid Crystal On Silicon).

The projection lens 24 is provided to project (perform magnifiedprojection of) the illumination light (the image light) modulated by thereflection-type liquid crystal device 21, onto the screen 30.

[Function and Effects of Display 3] (1. Display Operation)

In this display 3, first, the light (the laser beams) emitted from thered laser 11R, the green laser 11G, and the blue laser 11B arecollimated by the coupling lenses 12R, 12G, and 12B, respectively, tobecome the parallel beams in the illumination unit 1, as illustrated inFIG. 1. Then, each of the laser beams (the red laser beam, the greenlaser beam, and the blue laser beam) which have thus become the parallelbeams are subjected to the color composition (the optical pathsynthesis) by the dichroic prisms 131 and 132. Upon the optical pathsynthesis, each of the laser beams passes through the optical device 14,and is then collimated by the collimator lens 151 to become the parallelbeam. The parallel beam is then incident upon the fly-eye lens 152. Thisincident light is made uniform (the in-plane intensity distribution ismade uniform) by the fly-eye lens 152. The incident light made uniformis then outputted to be condensed by the condensing lens 153. In thisway, the illumination light is outputted from the illumination unit 1.

Subsequently, the illumination light is selectively reflected by thepolarization beam splitter 23, to be incident upon the reflection-typeliquid crystal device 21 through the field lens 22. In thereflection-type liquid crystal device 21, the incident light isreflected while being modulated based on the image signal, and therebythe incident light is outputted as the image light. Here, in thisreflection-type liquid crystal device 21, the polarized light whenincident and the polarized light when outputted are different.Therefore, the image light outputted from the reflection-type liquidcrystal device 21 passes through the polarization beam splitter 23selectively, and is then incident upon the projection lens 24. Thisincident light (the image light) is projected (subjected to themagnified projection) by the projection lens 24, onto the screen 30.

At this time, each of the red laser 11R, the green laser 11G, and theblue laser 11B performs intermittent emission of light at apredetermined emission frequency, for example. This allows each of thelaser beams (the red laser beam, the green laser beam, and the bluelaser beam) to be outputted sequentially in a time-divisional manner.Then, in the reflection-type liquid crystal device 21, the laser beam ofthe corresponding color is sequentially modulated in a time-divisionalmanner, based on the image signal of each of color components (a redcomponent, a green component, and a blue component). In this way, acolor image is displayed based on the image signals in the display 3.

(2. Light Receiving Operation, and Operation of Controlling Amount ofOutgoing Beam)

In this illumination unit 1, each of the laser beams incident from thered laser 11R, the green laser 11G, and the blue laser 11B upon thedichroic prism 132 is outputted, after being branched into the outgoingoptical path L1 of the illumination light and the light-receivingoptical path L2. The light flux traveling on the light-receiving opticalpath L2 is received by the photodetector 17 through the coupling lens12. Based on the quantity of this received light flux, the controlsection 18 controls the emitted light quantity in the red laser 11R, thegreen laser 11G, and the blue laser 11B. Specifically, the emitted lightquantity in each of the red laser 11R, the green laser 11G, and the bluelaser 11B is controlled by the control section 18 to be substantiallyconstant (desirably, constant) without depending on temperature changes.This stabilizes light-emitting operation in each of the red laser 11R,the green laser 11G, and the blue laser 11B. As a result, an improvementis made to color reproduction characteristics in displaying the image,and reductions in color unevenness as well as flickering are achieved.The quality of the displayed image is thereby enhanced.

(3. Function of Characteristic Part)

Next, function of a characteristic part (function of the illuminationunit 1) in the present embodiment will be described in detail, whilemaking a comparison with a comparative example.

First, the laser beam is generated by entrance of exciting light into alaser medium made of a laser crystal. An intensity distribution (a lightquantity distribution, FFP (Far Field Pattern)) of this laser beam isdetermined according to a distribution of atoms or molecules of thelaser crystal serving as the laser medium, and the size of the crystal.Ideally, the light quantity distribution of the generated laser beam issubstantially a Gaussian distribution, as illustrated in FIGS. 2A and2B, for example. In reality however, a light quantity distribution (aprofile) of a laser beam generated by a currently available laser iswhat is illustrated in FIGS. 3A and 3B, for example. In other words,unlike the one illustrated in FIGS. 2A and 2B, this light quantitydistribution is not a complete Gaussian distribution, and there arecracks appearing in the profile as well as in the vicinity of a peak,and side lobes are formed. It is to be noted that “horizontal” and“vertical” in each of FIG. 2B and FIG. 3B indicate the light quantitydistribution along the horizontal direction and that along the verticaldirection, respectively, and this indication will remain the samehereinafter. In a comparative example which will be described below,such an unstable (incomplete) light quantity distribution in the laserlight source results in a disadvantage, with regard to stabilization oflight-emitting operation by a photodetector 17 and a control section 18.

3-1. Comparative Example

FIG. 4 illustrates an overall configuration of a display (a display 103)according to the comparative example. The display 103 of thiscomparative example is a projection-type display that projects imagelight onto a screen 30, like the display 3 of the present embodiment.This display 103 includes an illumination unit 101 having no couplinglens 12, in place of the illumination unit 1 having the coupling lens12, and is otherwise similar in configuration to the display 3.

In the illumination unit 101 of this comparative example, thephotodetector 17 has a light-receiving surface 170 sufficiently smallerthan a cross-sectional area (a beam area) of a light flux traveling on alight-receiving optical path L2, as illustrated in FIG. 5, for example.This is to prevent detection of excess light such as stray light in anoptical path and light reflected from a reflection-type liquid crystaldevice 21.

Here, each of a red laser 11R, a green laser 11G, and a blue laser 11Bis assumed to have a light quantity distribution (a profile) similar tothat in FIGS. 3A and 3B. As illustrated in FIGS. 6A and 6B, for example,only a part (specifically, in the vicinity of a central part) of thelight quantity distribution in the light flux traveling on thelight-receiving optical path L2 is considered to be monitored on thelight-receiving surface 170 in the photodetector 17. It is to be notedthat this example is based on a model in which diverging rays outputtedfrom the red laser 11R, the green laser 11G, and the blue laser 11B arerespectively incident upon coupling lenses 12R, 12G, and 12B each havinga planoconvex spherical surface with an effective diameter ϕ of about 3mm. Thus, each of the diverging rays becomes an outgoing light flux witha diameter ϕ of about 3 mm. Further, this example is based on a model inwhich a light quantity is monitored by the light-receiving surface 170using the photodetector 17 with a diameter ϕ of about 0.5 mm, to achieveabout 1/10 of the beam area.

At this moment, as illustrated in FIGS. 7A, 7B, and 7C, for example, atemperature change occurs in the light quantity distribution of thelight flux traveling on the light-receiving optical path L2. Thistemperature change occurs because a change in the light quantitydistribution (the profile) of the laser beam emitted from a laser lightsource takes place according to the temperature (the temperature of thelaser light source). It is to be noted that FIGS. 7A, 7B, and 7Cillustrate the light quantity distribution of the light flux at thetemperature of the laser light source being 32° C., 37° C., and 43° C.,respectively. What is apparent from these figures is as follows. In apart (in the vicinity of a central part in the light flux) where thelight is received by the light-receiving surface 170 of thephotodetector 17, there is almost no change in the light quantitydistribution of the light flux, even when there is a change in thetemperature. On the other hand, in a part (in a peripheral part) wherethe light is not received by the light-receiving surface 170, the lightquantity distribution of the light flux changes in response to a changein the temperature. Specifically, although there is no change in thelight quantity distribution depending on the temperature in the vicinityof the central part, the light quantity in the peripheral part (aside-lobe part) decreases with increasing temperature. Therefore, in thelight flux as a whole, the light quantity decreases as the temperaturerises.

In this comparative example, there is almost no change in the lightquantity detected by the photodetector 17 even when the temperaturechange. Therefore, a temperature change in the quantity of the beamemitted from the laser light source is unlikely to be detected. As aresult, it is difficult to perform accurate light control (stabilizationof the light-emitting operation) with the control section 18, allowing achange in the quantity of the illumination light to be resulted from atemperature change in the light quantity distribution of the laser beam.

A temperature change rate in the light quantity distribution of thelaser beam as described above varies according to the wavelength of thelaser beam. Therefore, when the temperature changes following a state inwhich a color balance is adjusted at a certain temperature, the emittedlight quantity in the laser beam of each color also changes. Thus, aratio of mixing the laser beams of the respective colors also changes,making it difficult to maintain a desired color balance (a whitebalance).

3-2. Function of Present Embodiment

In contrast, in the illumination unit 1 of the present embodiment, thecoupling lens 12 functioning as the light-quantity-distribution controldevice (the refractive device with positive power) is provided betweenthe dichroic prism 132 and the photodetector 17 on the light-receivingoptical path L2, as illustrated in FIG. 1. Thus, the light quantitydistribution in the light flux to be incident upon the photodetector 17is controlled, and an average light quantity in the light quantitydistribution (an emitted light quantity distribution of the laser lightsource) of this incident light flux is incident upon the light-receivingsurface 170 in the photodetector 17.

In the illumination unit 101 of the comparative example, the light fluxtraveling on the light-receiving optical path L2 is directly incidentupon the photodetector 17 as the incident light flux, as illustrated inFIG. 8A, for example. As a result, on the light-receiving surface 170 inthe photodetector 17, only a part (in the vicinity of the central part)of the light quantity distribution in this incident light flux ismonitored, as illustrated in FIG. 9A, for example.

In contrast, in the illumination unit 1 of the present embodiment, afterthe light quantity in each of the vicinity of the central part and theperipheral part, in the light flux traveling on the light-receivingoptical path L2, is reduced by the coupling lens 12, the light flux isincident upon the photodetector 17 as the incident light, as in Example1 illustrated in FIG. 8B, for instance. As a result, the average lightquantity in the light quantity distribution of this incident light fluxis monitored on the light-receiving surface 170 in the photodetector 17,as illustrated in FIG. 9B, for example.

In this way, in the illumination unit 1, even when a change occurs inthe light quantity distribution in the laser beam emitted from each ofthe red laser 11R, the green laser 11G, and the blue laser 11B dependingon the temperature (even when the profile of the light quantitydistribution varies), the light quantity distribution in the light fluxincident upon the photodetector 17 is unlikely to vary. Therefore, inthe illumination unit 1, there is an improvement in the accuracy ofcontrolling the emitted light quantity in the red laser 11R, the greenlaser 11G, and the blue laser 11B by the control section 18.

In the present embodiment, the light-quantity-distribution controldevice (the coupling lens 12) that controls the light quantitydistribution in the light flux to be incident upon the photodetector 17is provided between the dichroic prism 132 and the photodetector 17 onthe optical path (the light-receiving optical path L2) different fromthe outgoing optical path L1 of the illumination light. Therefore, in acase where a change occurs in the light quantity distribution of thelaser beam depending on the temperature, the accuracy of controlling theemitted light quantity in the red laser 11R, the green laser 11G, andthe blue laser 11B is allowed to be improved. Thus, light-quantityvariations in the illumination light emitted from the illumination unit1 are allowed to be reduced. As a result, even when an existing laserlight source with an incomplete beam profile is used, a projectorsystem, which is capable of performing stable image display withoutbeing affected by perturbations such as the temperature, is allowed tobe implemented. Moreover, the ratio of mixing the laser beams of therespective colors is prevented from changing, and thereby a desiredcolor balance (a white balance) is maintained.

In addition, the coupling lens 12 allows the light in a side-lobe regionwhere a variation in the light source profile occurs to be alsocondensed and received by the photodetector 17. Thus, almost all thelight-quantity variations, which result from variations in the profilecaused by changes in the temperature, are detected by the photodetector17. Moreover, the size of the light-receiving surface 170 in thephotodetector 17 remains the same as that of an existing (ordinary) oneand therefore, a configuration unaffected by the stray light isrealized.

Now, other embodiments (second to fifth embodiments) according to thedisclosure will be described. The same elements as those of the firstembodiment will be provided with the same characters as those of thefirst embodiment, and the description thereof will be omitted asappropriate.

Second Embodiment

FIG. 10 illustrates an overall configuration of a display (a display 3A)according to the second embodiment. The display 3A of the presentembodiment is configured by providing an illumination unit 1A to bedescribed below, in place of the illumination unit 1 in the display 3 ofthe first embodiment. The display 3A is otherwise similar inconfiguration to the display 3.

The illumination unit 1A is configured by providing a diffusion device12A to be described below, in place of the coupling lens 12 in theillumination unit 1 of the first embodiment. The illumination unit 1A isotherwise similar in configuration to the illumination unit 1.

The diffusion device 12A is disposed between a dichroic prism 132 and aphotodetector 17 on a light-receiving optical path L2, like the couplinglens 12. As in Example 2 illustrated in FIG. 11A, for example, thediffusion device 12A diffuses a light flux traveling on thelight-receiving optical path L2, and outputs the diffused light flux.This allows the diffusion device 12A to control a light quantitydistribution in a light flux to be incident upon the photodetector 17,in a manner similar to the coupling lens 12. As a result, an averagelight quantity in the light quantity distribution of this incident lightflux is monitored on the light-receiving surface 170 in thephotodetector 17, as illustrated in FIG. 11B, for example. In otherwords, this diffusion device 12A also corresponds to a specific but notlimitative example of “light-quantity-distribution control device” inthe technology.

Further, since such a diffusion device 12A is provided, a side-lobe partof the incident light flux, in which part the light quantity changesgreatly, is incident upon the photodetector 17 in a constant proportion,in a manner similar to a main light flux in the vicinity of a centralpart. This is illustrated in Example 2 depicted in FIG. 12B and FIG.13B, for example. Therefore, it is possible to address such adisadvantage that an emitted light quantity traveling on an outgoingoptical path L1 is unlikely to be held constant, because of a partialvariation in a light quantity distribution. It is to be noted that inthe comparative example described above, in contrast, the diffusiondevice 12A is not provided and thus, the side-lobe part where the lightquantity changes greatly is not incident upon the photodetector 17, asillustrated in FIG. 12A and FIG. 13A, for example.

In the present embodiment, the light-quantity-distribution controldevice (the diffusion device 12A), which controls the light quantitydistribution in the light flux to be incident upon the photodetector 17,is provided between the dichroic prism 132 and the photodetector 17 onthe optical path (the light-receiving optical path L2) different fromthe outgoing optical path L1 of the illumination light. Therefore,effects similar to those of the first embodiment are achievable. Inother words, in a case where there is a change in the light quantitydistribution of the laser beam depending on the temperature, theaccuracy of controlling an emitted light quantity for a red laser 11R, agreen laser 11G, and a blue laser 11B is improved, and variations in thelight-quantity in the illumination light outputted from the illuminationunit 1A are allowed to be reduced.

Third Embodiment [Configuration of Display 3B]

FIG. 14 illustrates an overall configuration of a display (a display 3B)according to the third embodiment. The display 3B of the presentembodiment is configured by providing an illumination unit 1B to bedescribed below, in place of the illumination unit 1 in the display 3 ofthe first embodiment. The display 3B is otherwise similar inconfiguration to the display 3.

The illumination unit 1B is configured by further providing a polarizingdevice 16 which will be described below, between the dichroic prism 132and the photodetector 17 on the light-receiving optical path L2 in theillumination unit 1 of the first embodiment. The illumination unit 1B isotherwise similar in configuration to the illumination unit 1.Specifically, in the present embodiment, the polarizing device 16 isdisposed between a dichroic prism 132 and a coupling lens 12 on alight-receiving optical path L2, for instance.

The polarizing device 16 is disposed between the dichroic prism 132 anda photodetector 17 (specifically, between the dichroic prism 132 and thecoupling lens 12) on the light-receiving optical path L2. Thispolarizing device 16 controls polarized components so that the samepolarized component as a main polarized component (here an S-polarizedlight component) in illumination light relatively increases, in a lightflux traveling on the light-receiving optical path L2. The polarizingdevice 16 corresponds to a specific but not limitative example of“optical member” in the disclosure. Specifically, as illustrated in FIG.14, the polarizing device 16 selectively removes the polarized component(a P-polarized light component) different from the main polarizedcomponent, while selectively allowing the same polarized component (anS-polarized light component) as the main polarized component in theillumination light in the light flux traveling on the light-receivingoptical path L2 to pass therethrough.

[Function and Effects of Display 3B]

In this display 3B, the following function and effects are achieved byproviding the polarizing device 16 in the illumination unit 1B. First,there will be described a disadvantage ascribable to the difference intemperature characteristics (a light-quantity change rate in response toa temperature change) between the polarized components (the S-polarizedlight component and the P-polarized light component) in a laser beamemitted from each of a red laser 11R, a green laser 11G, and a bluelaser 11B.

(Disadvantage Ascribable to Difference in Temperature CharacteristicsBetween Polarized Components)

FIGS. 15A and 15B each illustrate an example of a light quantitydistribution (a profile) in the laser beam emitted from each of the redlaser 11R, the green laser 11G, and the blue laser 11B. Specifically,FIGS. 15A and 15B depict the P-polarized light component and theS-polarized light component, respectively. According to these lightquantity distributions, the P-polarized light component illustrated inFIG. 15A is present mainly in a side-lobe region (a peripheral part) inthe light flux, but is hardly present in the vicinity of a central part.On the other hand, the S-polarized light component illustrated in FIG.15B is present mainly in the vicinity of the central part in the lightflux, while being hardly present in the side-lobe region.

In the laser beam emitted from each of the red laser 11R, the greenlaser 11G, and the blue laser 11B, the polarized components usuallyexist at a ratio of the S-polarized light component to the P-polarizedlight component=ls:lp=95:5. In the comparative example describedearlier, only the light quantity in the vicinity of the central part ofthe light flux traveling on the light-receiving optical path L2 ismonitored. Therefore, the P-polarized light component is not incidentupon the photodetector 17, and only the light quantity of the polarizedcomponent (the S-polarized light component) same as that in the lightflux traveling on the outgoing optical path L1 of the illumination lightis allowed to be monitored. However, when the average light quantity inthe light quantity distribution of this light flux is monitored in thephotodetector 17 as in the first and second embodiments, both theS-polarized light component and the P-polarized light component areincident upon the photodetector 17. Thus, the following issue arises asa result of the difference in temperature characteristics between thesepolarized components.

Here, as an example, there will be described a relationship between thelight quantity for each polarized component in the laser beam emittedfrom each of the laser light sources (i.e. the quantity of the lightemitted from the light source), and an optical reflectance (a prismreflectance) as well as an optical transmittance (a prism transmittance)for each polarized component in the dichroic prism 132, as illustratedin FIG. 16. Specifically, there will be described a ratio between thelight quantity of the illumination light (the light flux traveling onthe outgoing optical path L1) and the light quantity of the light fluxtraveling to the photodetector 17 (on the light-receiving optical pathL2). This ratio is ascribable to the above-mentioned relationship.

At first, in the dichroic prism 132, the optical reflectance for theS-polarized light component, of which light quantity is dominant in theemitted laser beam as described above, is relatively higher than theoptical reflectance for the P-polarized light component, so that thelaser beam emitted from each of the laser light sources is handledefficiently as the illumination light. Specifically, as illustrated inFIG. 16, reflection and transmission characteristics in a reflectiontransmission film 130 are set to provide about 95% (0.95) of a prismreflectance Rs for the S-polarized light component, and about 25% (0.25)of a prism reflectance Rp for the P-polarized light component. Further,a prism transmittance (1−Rs) for the S-polarized light component isabout 5% (0.05), and a prism transmittance (1−Rp) for the P-polarizedlight component is about 75% (0.75). Here, the light quantity of each ofthe light fluxes after light-path branching in this dichroic prism 132is also illustrated in FIG. 16, assuming that the quantity of the lightemitted from the light source is about 100%, in the case of ls:lp=about95:5 as mentioned above. In other words, in the light quantity of theillumination light, the polarized components are distributed at theratio between the S-polarized light component to the P-polarized lightcomponent=about 72.2:1, and thus, the S-polarized light component isdominant. On the other hand, in the light quantity of the light fluxtraveling to the photodetector 17, the polarized components aredistributed at the ratio between the S-polarized light component and theP-polarized light component=about 1.27:1. Therefore, the proportion ofthe P-polarized light component being present is considerably high, ascompared with the light quantity of the illumination light. Bearing thisrelationship in mind, the difference in temperature characteristics (thelight-quantity change rate in response to a temperature change) betweenthe polarized components will be described below.

First, in general, the quantity of an emitted laser beam when a constantcurrent is fed decreases by about 10% at 38° C., under the influence ofa heat resulting from a temperature rise, as compared with that at 28°C., as illustrated in FIG. 17, for example. Here, as illustrated in FIG.17, the light quantity of the S-polarized light component of the laserbeam emitted from the laser light source decreases by about 10% asmentioned above, when the temperature rises from 28° C. to 38° C. (arate of change=about 0.91). In contrast, the light quantity of theP-polarized light component of the laser beam emitted from the laserlight source decreases by about 20%, when the temperature rises from 28°C. to 38° C. (a rate of change=about 0.81). In other words, a behaviorin response to the temperature of the P-polarized light component isdifferent from a behavior in response to the temperature of theS-polarized light component. It is to be noted that each temperaturesillustrated in FIG. 17 is the temperature of a laser tube package itselfat the time of emitting the laser beam, and each emitted light quantityis an actual value.

Because of the difference between such behaviors in response to thetemperatures for the respective polarized components, a difference intemperature characteristic (the light-quantity change rate in responseto the temperature change) between the polarized components occurs in areal projector, which will be described as follows. The illuminationlight, which is present at a light quantity ratio of the S-polarizedlight component to the P-polarized light component=about 4.75:3.75=about72.2:1, mainly contains the S-polarized light component as describedabove. Therefore, about 9% decrease in the light quantity occurs whenthe temperature change ΔT is 10° C. ((Δls/ΔT)=(0.91/10)=0.091). On theother hand, as described above, in the light flux traveling to thephotodetector 17 existing at a light quantity ratio of the S-polarizedlight component to the P-polarized light component=about90.25:1.25=about 1.27:1, about 19% decrease in the light quantity occurswhen the temperature change ΔT is 10° C. ((Δlp/ΔT)=(0.81/10)=0.081).Therefore, about 14% decrease in the light quantity occurs, as expressedby the following expression (1), because the P-polarized light componentand the S-polarized light component are mixed.

(4.75×0.91+3.75×0.81)/(4.75+3.75)=0.86  (1)

Thus, the decline (about 14%) in the light quantity detected on thephotodetector 17 side is greater than the decline (about 9%) in thelight quantity occurring on the actual illumination light side.Therefore, overcorrection takes place in the light control by thecontrol section 18, and the light quantity of the illumination lightbecomes more (brighter) than necessary. In addition, a correction driftrate when the temperature change ΔT is 10° C. is about (0.91/0.86)=1.06in the temperature rise from 28° C. to 38° C. mentioned above, but thecorrection drift rate further increases in environments at temperatureshigher and lower than that. Specifically, for instance, in a case of usein an environment at a high-temperature of 60° C., an influence thereofis about (60/25)=2.4-fold and therefore, a change of about (6×2.4)=14%to 15% occurs in the quantity of the illumination light. This makes itdifficult to achieve stable operation.

(Operation of Present Embodiment)

Therefore, in the present embodiment, the polarizing device 16 isprovided in the illumination unit 1B as described above. The polarizingdevice 16 controls the polarized components so that the same polarizedcomponent as the main polarized component (here, the S-polarized lightcomponent) in the illumination light relatively increases in the lightflux traveling on the light-receiving optical path L2. Specifically,here, as illustrated in FIG. 14, the polarizing device 16 selectivelyallows, of the light flux traveling on the light-receiving optical pathL2, the polarized component (the S-polarized light component) same asthe main polarized component in the illumination light to passtherethrough. At the same time, the polarizing device 16 removes thepolarized component (the P-polarized light component) different from themain polarized component.

As a result, in the illumination unit 1B, the light quantitydistribution in the light flux to be incident upon the photodetector 17is less likely to vary, even when there occurs, in addition to thechange of the light quantity distribution in the laser beam emitted fromthe laser light source depending on the temperature, the difference intemperature characteristics (the light-quantity change rate in responseto the temperature change) between the respective polarized componentsincluded in the laser beam. Therefore, in the illumination unit 1B, afurther improvement is made in the accuracy of controlling the emittedlight quantity for the red laser 11R, the green laser 11G, and the bluelaser 11B by the control section 18.

In the present embodiment, as described above, there is provided thepolarizing device 16 that controls the polarized components so that thesame polarized component as the main polarized component in theillumination light relatively increases, in the light flux traveling onthe light-receiving optical path L2. Therefore, the accuracy ofcontrolling the emitted light quantity is further improved, as comparedwith those in the first and second embodiments. Hence, thelight-quantity variations in the illumination light are further reduced.

It is to be noted that in the present embodiment, there has beendescribed the case where the coupling lens 12 in the first embodiment isemployed as the “light-quantity-distribution control device”, althoughit is not limited thereto. For example, the diffusion device 12A in thesecond embodiment may be used. This also applies to fourth and fifthembodiments which will be described below.

Fourth Embodiment

FIG. 18 illustrates an overall configuration of a display (a display 3C)according to the fourth embodiment. The display 3C of the presentembodiment is configured by providing an illumination unit 1C to bedescribed below, in place of the illumination unit 1 in the display 3 ofthe first embodiment. The display 3C is otherwise similar inconfiguration to the display 3.

The illumination unit 1C is configured by providing a reflectiontransmission film 130C to be described below, in place of the reflectiontransmission film 130 in the dichroic prism 132 of the illumination unit1 in the first embodiment. The illumination unit 1C is otherwise similarin configuration to the illumination unit 1.

The reflection transmission film 130C controls polarized components sothat the same polarized component as a main polarized component (here anS-polarized light component) in illumination light relatively increasesin a light flux traveling on a light-receiving optical path L2, in amanner similar to the polarizing device 16 in the third embodiment. Inother words, in the present embodiment, a dichroic prism 132 having thisreflection transmission film 130C corresponds to a specific but notlimitative example of “optical member” in the disclosure. Specifically,unlike the reflection transmission film 130 described above, thereflection transmission film 130C is set so that each of an opticalreflectance (a prism reflectance) and an optical transmittance (a prismtransmittance) in the dichroic prism 132 becomes substantially constant(desirably, constant), without depending on the polarized components. Itis to be noted that such reflection and transmission characteristics arerealized by, for example, making adjustments to materials of thereflection transmission film 130C (such as adjustments to a material anda film thickness of each layer, the number of laminated layers, and thelike in a multilayer film made of the dielectric materials mentionedabove).

Specifically, in an example illustrated in FIG. 19, the reflection andtransmission characteristics in the reflection transmission film 130Care set to have about 95% (0.95) of a prism reflectance Rp for anP-polarized light component, which is equal to a prism reflectance Rsfor a S-polarized light component, unlike the reflection transmissionfilm 130 described above. Also unlike the reflection transmission film130, the reflection and transmission characteristics in the reflectiontransmission film 130C are set to have about 5% (0.05) of a prismtransmittance (1−Rs) for the S-polarized light component, which is equalto a prism transmittance (1−Rp) for the P-polarized light component.

Thus, in the present embodiment, the light quantity is distributed atthe ratio of the S-polarized light component to the P-polarized lightcomponent=19:1, for both the quantity of the illumination light and thequantity of the light flux traveling to the photodetector 17, asillustrated in FIG. 19, for example. As a result, between the quantityof the illumination light and the quantity of the light flux travelingto the photodetector 17, there is no difference in temperaturecharacteristic (a light-quantity change rate in response to atemperature change) based on each polarized component. Therefore, thelight quantity distribution in the light flux to be incident upon thephotodetector 17 is less likely to vary in the illumination unit 1C ofthe present embodiment as well, even when there occurs, in addition to achange of the light quantity distribution in a laser beam emitted from alaser light source depending on the temperature, a difference intemperature characteristic (the light-quantity change rate in responseto the temperature change) between the respective polarized componentsincluded in the laser beam. Therefore, in the illumination unit 1C, afurther improvement is made in the accuracy of controlling an emittedlight quantity for a red laser 11R, a green laser 11G, and a blue laser11B by a control section 18.

In the present embodiment, the dichroic prism 132 having the reflectiontransmission film 130C which controls the polarized components so thatthe same polarized component as the main polarized component in theillumination light relatively increases, in the light flux traveling onthe light-receiving optical path L2, as described above. Therefore, theaccuracy of controlling the emitted light quantity is further improved,as compared with those in the first and second embodiments. Hence,variations in the light-quantity in the illumination light are furtherreduced.

Moreover, in the present embodiment, only making an adjustment to thereflection and transmission characteristics in the reflectiontransmission film 130C is necessary, and a member like the polarizingdevice 16 is not necessarily added. Therefore, the cost of members isallowed to be reduced, as compared with the third embodiment.

Fifth Embodiment

FIG. 20 illustrates an overall configuration of a display (a display 3D)according to the fifth embodiment. The display 3D of the presentembodiment is configured by providing an illumination unit 1D to bedescribed below, in place of the illumination unit 1 in the display 3 ofthe first embodiment. The display 3D is otherwise similar inconfiguration to the display 3.

The illumination unit 1D is configured by providing a reflectiontransmission film 130D to be described below, in place of the reflectiontransmission film 130 in the dichroic prism 132 of the illumination unit1 in the first embodiment. The illumination unit 1D is otherwise similarin configuration to the illumination unit 1.

(Reflection Transmission Film 130D)

The reflection transmission film 130D controls polarized components sothat the same polarized component as a main polarized component (here,an S-polarized light component) in illumination light relativelyincreases, in a light flux traveling on a light-receiving optical pathL2, in a manner similar to the polarizing device 16 and the reflectiontransmission film 130C. In other words, in the present embodiment, adichroic prism 132 having this reflection transmission film 130Dcorresponds to a specific but not limitative example of “optical member”in the disclosure.

Specifically, in this reflection transmission film 130D, each of anoptical reflectance (a prism reflectance) and an optical transmittance(a prism transmittance) is set as follows, unlike the reflectiontransmission films 130 and 130C described above. Specifically, each ofthe prism reflectance and the prism transmittance is set for eachpolarized component, so that a temperature change rate in a reflectedlight quantity and a temperature change rate in a transmitted lightquantity in the dichroic prism 132 are substantially equal to each other(desirably, equal to each other). To be more specific, each of the prismreflectance and the prism transmittance is set so that the amount of adifference between the temperature change rate in the reflected lightquantity and the temperature change rate in the transmitted lightquantity falls within a predetermined range (e.g., about 10% or less),as will be described below. This makes it possible to address adifference in temperature characteristics (a light-quantity change ratein response to a temperature change) between the respective polarizedcomponents included in a laser beam, even when it is difficult toequalize reflection and transmission characteristics in the dichroicprism 132 for each of the polarized components as in the fourthembodiment. It is to be noted that such reflection and transmissioncharacteristics are realized by, for example, making adjustments tomaterials of the reflection transmission film 130D (such as adjustmentsto a material and a film thickness of each layer, the number oflaminated layers, and the like in a multilayer film made of thedielectric materials mentioned above).

Here, a specific example (Example 3) of the dichroic prism 132 havingsuch a reflection transmission film 130D of the present embodiment willbe described in detail. It is to be noted that the following descriptionis provided, assuming that, of a laser beam incident from a laser lightsource upon the dichroic prism 132, a light flux reflected by thedichroic prism 132 travels on a outgoing optical path L1 (towards aprojection lens 24), and a light flux passing through the dichroic prism132 travels on the light-receiving optical path L2 (towards aphotodetector 17). A technique using a similar idea is applicable to theopposite case.

First, FIGS. 21(A), 21(B), 21(C) and 21(D) illustrate an example of arelationship between a polarization component ratio in the emitted laserbeam and an optical reflectance for each polarized component in thedichroic prism 132 (the reflection transmission film 130D). Therelationship is provided with respect to each of the light fluxtraveling to the photodetector 17 and the light flux traveling to theprojection lens 24. Specifically, FIG. 21(A) illustrates therelationship between the polarization component ratio in the emittedlaser beam and the optical reflectance (an S reflectance) for theS-polarized light component in the dichroic prism 132, with respect tothe light flux traveling to the photodetector 17. What is illustrated inthis FIG. 21(A) corresponds to the light quantity of the S-polarizedlight component in the light flux traveling to the photodetector 17,which is defined by an expression (2) listed below. In addition, FIG.21(C) illustrates the relationship between the polarization componentratio in the emitted laser beam and the optical reflectance (a Preflectance) for the P-polarized light component in the dichroic prism132, with respect to the light flux traveling to the photodetector 17.What is illustrated in this FIG. 21(C) corresponds to the light quantityof the P-polarized light component in the light flux traveling to thephotodetector 17, which is defined by an expression (3) listed below. Onthe other hand, FIG. 21(B) illustrates the relationship between thepolarization component ratio in the emitted laser beam and the Sreflectance in the dichroic prism 132, with respect to the light fluxtraveling to the projection lens 24. What is illustrated in this FIG.21(B) corresponds to the light quantity of the S-polarized lightcomponent in the light flux traveling to the projection lens 24, whichis defined by an expression (4) listed below. In addition, FIG. 21(D)illustrates the relationship between the polarization component ratio inthe emitted laser beam and the P reflectance in the dichroic prism 132,with respect to the light flux traveling to the projection lens 24. Whatis illustrated in this FIG. 21(D) corresponds to the light quantity ofthe P-polarized light component in the light flux traveling to theprojection lens 24, which is defined by an expression (5) listed below.From these FIGS. 21(A), 21(B), 21(C) and 21(D), it is apparent that eachof the light quantity of the light flux traveling to the photodetector17 and the light quantity of the light flux traveling to the projectionlens 24 changes according to the polarization component ratio in theemitted laser beam and the optical reflectance for each of the polarizedcomponents in the dichroic prism 132.

ls×(1−Rs)  (2)

lp×(1−Rp)  (3)

ls×Rs  (4)

lp×Rp  (5)

FIGS. 22(A) and 22(B) illustrate an example of the relationship betweenthe polarization component ratio in the emitted laser beam and theoptical reflectance for each of the polarized components in the dichroicprism 132 (the reflection transmission film 130D) at a normaltemperature (about 25° C.). This relationship is provided for each ofthe light flux traveling to the photodetector 17 and the light fluxtraveling to the projection lens 24. Specifically, FIG. 22(A)illustrates the relationship between the polarization component ratio inthe emitted laser beam and the P reflectance in the dichroic prism 132at the normal temperature, with respect to the light flux traveling tothe photodetector 17. What is illustrated in this FIG. 22(A) correspondsto the light quantity of (P-polarized light component+S-polarized lightcomponent) in the light flux traveling to the photodetector 17 at thenormal temperature, which is defined by an expression (6) listed below.In addition, FIG. 22(B) illustrates the relationship between thepolarization component ratio in the emitted laser beam and the Preflectance in the dichroic prism 132 at the normal temperature, withrespect to the light flux traveling to the projection lens 24. What isillustrated in this FIG. 22(B) corresponds to the light quantity of(P-polarized light component+S-polarized light component) in the lightflux traveling to the projection lens 24 at the normal temperature,which is defined by an expression (7) listed below. It is to be notethat, in the following, the S reflectance in the dichroic prism 132 isassumed to be fixed at about 95%, because the S-polarized lightcomponent is dominant in the polarized components in the emitted laserbeam as described above.

D={ls×(1−Rs)}+{lp×(1−Rp)}  (6)

B=(ls×Rs)+(lp×Rp)  (7)

FIGS. 22(C) and 22(D) illustrate an example of the relationship betweenthe polarization component ratio in the emitted laser beam and theoptical reflectance for each of the polarized components in the dichroicprism 132 (the reflection transmission film 130D), at a high temperature(substantially, 25° C.+ΔT (10° C.)=35° C.). This relationship isprovided for each of the light flux traveling to the photodetector 17and the light flux traveling to the projection lens 24. Specifically,FIG. 22(C) illustrates the relationship between the polarizationcomponent ratio in the emitted laser beam and the P reflectance in thedichroic prism 132 at the high temperature, with respect to the lightflux traveling to the photodetector 17. What is illustrated in this FIG.22(C) corresponds to the light quantity of (P-polarized lightcomponent+S-polarized light component) in the light flux traveling tothe photodetector 17 at the high temperature, which is defined by anexpression (8) listed below. In addition, FIG. 22(D) illustrates therelationship between the polarization component ratio in the emittedlaser beam and the P reflectance in the dichroic prism 132 at the hightemperature, with respect to the light flux traveling to the projectionlens 24. What is illustrated in this FIG. 22(D) corresponds to the lightquantity of (P-polarized light component+S-polarized light component) inthe light flux traveling to the projection lens 24 at the hightemperature, which is defined by an expression (9) listed below. It isto be noted that in this calculation is based on (Δls/ΔT)=0.09 and(Δlp/ΔT)=0.08, using experimental values as an example. In addition,depending on a heat radiation design in the laser light source,individual differences occur in the change of an ambient temperature andthe temperature change of the laser light source itself. However, in themost cases, the change of an environmental temperature and thetemperature change of the laser light source itself serving as aheat-producing section are substantially the same which is ΔT, in astable condition. Further, the temperature change ΔT in the followingexpressions is assumed to be the temperature change of the laser lightsource itself, which occurs in response to the influence of a change inthe environmental temperature or a temperature change caused by otherheat-producing component.

$\begin{matrix}\left\lbrack {{Mathematical}\mspace{14mu} {Expression}\mspace{14mu} 1} \right\rbrack & \; \\{\quad\begin{matrix}\left\{ \begin{matrix}{C = {\left\lbrack {\left\{ {{Is} \times \left( {1 - {Rs}} \right)} \right\} \times \left( {\Delta \; {{Is}/\Delta}\; T} \right) \times \Delta \; T} \right\rbrack +}} & {\mspace{225mu} (8)} \\\left\lbrack {\left\{ {{Ip} \times \left( {1 - {Rp}} \right)} \right\} \times \left( {\Delta \; {{Ip}/\Delta}\; T} \right) \times \Delta \; T} \right\rbrack & \; \\{A = {\left\lbrack {\left( {{Is} \times {Rs}} \right) \times \left( {\Delta \; {{Is}/\Delta}\; T} \right) \times \Delta \; T} \right\rbrack +}} & {\mspace{230mu} (9)} \\\left\lbrack {\left( {{Ip} \times {Rp}} \right) \times \left( {\Delta \; {{Ip}/\Delta}\; T} \right) \times \Delta \; T} \right. & \;\end{matrix} \right. & \;\end{matrix}} & \;\end{matrix}$

ΔT: Temperature change in laser

(Δls/ΔT): Rate of change in emitted light quantity caused by temperaturechange of S-polarized light component

(Δlp/ΔT): Rate of change in emitted light quantity caused by temperaturechange of P-polarized light component

FIG. 23(A) illustrates a ratio defined by (a value in FIG. 22(C)/a valuein FIG. 22(A)). This ratio corresponds to a light-quantity change rateof the light flux traveling to the photodetector 17 at the time of thetemperature change (i.e. the temperature change rate in the transmittedlight quantity). Further, FIG. 23(B) illustrates a ratio defined by (avalue in FIG. 22(D)/a value in FIG. 22(B)). This ratio corresponds to alight-quantity change rate of the light flux traveling to the projectionlens 24 at the time of the temperature change (i.e. the temperaturechange rate in the reflected light quantity).

FIG. 23(C) illustrates a ratio defined by (a value in FIG. 23(B)/a valuein FIG. 23(A)) at the time of ΔT=25° C. This ratio corresponds to theamount of difference between the temperature change rate in thereflected light quantity and the temperature change rate in thetransmitted light quantity described above. Specifically, in thisexample, this ratio corresponds to the amount of difference defined by(the temperature change rate in the reflected light quantity/thetemperature change rate in the transmitted light quantity). It is to benoted that a gray part region illustrated in FIG. 23(C) is a regionwhere this amount of difference falls within a predetermined range(here, about 10% or less). In other words, when the amount of differencein FIG. 23(C) is 0 (zero), the light quantity of the light fluxtraveling to the projection lens 24 and the light quantity of the lightflux traveling to the photodetector 17 are equal to each other, withoutdepending on the temperature change, and there is no light-quantityvariation in the illumination light. On the other hand, when the amountof difference in FIG. 23(C) is other than 0, a light-quantity variationin the illumination light occurs according to the extent of the amountof difference. It is to be noted that, here, an initial adjustment inthe laser light source is made at the normal temperature (about 25° C.),and use in a temperature range from about 0° C. to about 50° C. isassumed. Further, the amount of difference is assumed to be maximum atthe time of the temperature change ΔT=25° C. Therefore, the values areindicated at the time of the temperature change ΔT=25° C.

For this reason, in the present embodiment, the prism reflectance andthe prism transmittance for each of the polarized components in thereflection transmission film 130D are set, so that the temperaturechange rate in the reflected light quantity and the temperature changerate in the transmitted light quantity in the dichroic prism 132 aresubstantially equal to each other (desirably, equal to each other), asdescribed above. Specifically, the prism reflectance and the prismtransmittance are set so that the amount of difference between thetemperature change rate of the reflected light quantity and thetemperature change rate of the transmitted light quantity falls withinthe predetermined range (e.g., about 10% or less). It is to be notedthat this 10% which is an example of the upper limit in the amount ofdifference is a value determined by the following reasons. First of all,in general, the life of a projector is defined as the time before thebrightness (luminance) of display light (illumination light) decreasesto about 50% of an initial value. However, the performance contributingto the brightness, such as an optical transmittance and an opticalreflectance in each component of the projector is assumed to decline byabout 10% of an initial value. Therefore, it may be said that it isappropriate to suppress the amount of difference to about 10%, also fora part depending on a temperature change that is a cause of an intensityvariation. In addition, it is known from an empirical rule that thehuman being is able to sensitively detect a discontinuous intensitychange. On the other hand, as for an intensity change in which theintensity gradually changes according to the temperature or the likevarying over some time, the detectivity of the human being is low, evenwhen the intensity change is about 10%. It is appropriate to set about10% of the amount of difference as a tolerance (a design margin) for theintensity change, in this respect as well.

This is expressed by expressions (10) or (11) listed below, using eachof the values A to D defined by the above expressions (6) to (9). Here,the expression (10) corresponds to an expression in a case in which thelight flux reflected from the dichroic prism 132 travels to theprojection lens 24, and the light flux passing through the dichroicprism 132 travels to the photodetector 17 as described above. On theother hand, the expression (11) corresponds to an expression in a casein which, conversely, the light flux passing through the dichroic prism132 travels to the projection lens 24, and the light flux reflected fromthe dichroic prism 132 travels to the photodetector 17. It is to benoted that FIG. 24 illustrates a relationship between the temperaturechange rate in the light quantity and the reflectance for theP-polarized light component in the dichroic prism according to thisExample 3.

$\begin{matrix}\left\lbrack {{Mathematical}\mspace{14mu} {Expression}\mspace{14mu} 2} \right\rbrack & \; \\\left\{ \begin{matrix}{0.9 \leqq \left\lbrack \frac{\left( {A/B} \right)}{\left( {C/D} \right)} \right\rbrack \leqq 1.1} & \left( {{when}\mspace{14mu} {the}\mspace{14mu} {transmitted}\mspace{14mu} {light}\mspace{14mu} {is}} \right. & {\mspace{40mu} (10)} \\\; & \left. {{incident}\mspace{14mu} {upon}\mspace{14mu} {the}\mspace{14mu} {photodetector}} \right) & \; \\{0.9 \leqq \left\lbrack \frac{\left( {C/D} \right)}{\left( {A/B} \right)} \right\rbrack \leqq 1.1} & \left( {{when}\mspace{14mu} {the}\mspace{14mu} {reflected}\mspace{14mu} {light}\mspace{14mu} {is}} \right. & {\mspace{40mu} (11)} \\\; & \left. {{incident}\mspace{14mu} {upon}\mspace{14mu} {the}\mspace{14mu} {photodetector}} \right) & \;\end{matrix} \right. & \;\end{matrix}$

In the present embodiment, the dichroic prism 132 having the reflectiontransmission film 130D is provided. The reflection transmission film130D controls the polarized components so that the same polarizedcomponent as the main polarized component in the illumination lightrelatively increases in the light flux traveling on the light-receivingoptical path L2. Therefore, even when there occurs, in addition to thechange of the light quantity distribution in the laser beam emitted fromthe laser light source depending on the temperature, the difference intemperature characteristics (the light-quantity change rate in responseto the temperature change) between the polarized components included inthe laser beam, the light quantity distribution in the light flux to beincident upon the photodetector 17 is less likely to vary. Therefore, ascompared with the first and second embodiments, the accuracy ofcontrolling the emitted light quantity is further improved, and thelight-quantity variations in the illumination light are further reduced.

In addition, only making an adjustment to the reflection andtransmission characteristics in the reflection transmission film 130D isnecessary, and a member like the polarizing device 16 is not necessarilyadded, in the present embodiment as well. Thus, the cost of members isreduced, as compared with the third embodiment.

[Modifications]

The technology of the disclosure has been described with reference tothe embodiments, but is not limited to these embodiments, and may bevariously modified.

For example, in the embodiments, the coupling lens 12 and the diffusiondevice 12A are each taken as an example of thelight-quantity-distribution control device, although it is not limitedto these examples. Alternatively, other device may be used as thelight-quantity-distribution control device. Likewise, in theembodiments, the polarizing device 16 and the dichroic prism 132 havingthe reflection transmission film 130C or 130D are each taken as anexample of the optical member, although it is not limited to theseexamples. Alternatively, other member may be used as the optical member.

Further, in the embodiments, the case where the main polarized componentin the illumination light is the S-polarized light component has beendescribed. However, the technology is not limited to this case, and isapplicable to a case where the main polarized component in theillumination light is the P-polarized light component, conversely.

Furthermore, in the embodiments, the case where each of the plural kindsof light source (for red, green, and blue) serves as the laser lightsource has been described, although the technology is not limited tothis case. The technology is applicable to any case, as long as one ormore of the plural kinds of light source are provided as the laser lightsource. For instance, the laser light source and other type of lightsource (e.g., LED) may be combined and provided in the light sourcesection.

In addition, in the embodiments, the case where the light modulationdevice is the reflection-type liquid crystal device has been describedas an example, although the technology is not limited to this case. Thelight modulation device may be a transmissive liquid crystal device, ormay be a light modulation device other than the liquid crystal device(e.g., DMD (Digital Micromirror Device)).

Still furthermore, in the embodiments, the case where the three kinds oflight sources emitting light of different wavelengths has beendescribed. However, one kind, or two kinds, or four or more of kinds oflight sources may be used, for example.

Moreover, in the embodiments, each component (optical system) of theillumination unit and the display has been described as a specificexample. However, it is not necessary to provide all the components, orother components may be further provided. Specifically, for example, adichroic mirror may be provided in place of the dichroic prisms 131 and132.

In addition, in the embodiments, there has been described the case wherethe projection-type display having the projection optical system (theprojection lens) that projects the light modulated by the lightmodulation device onto the screen is configured. However, the technologyis applicable to a direct-viewing-type display.

It is to be noted that the technology may be configured as follows.

(1) An illumination unit including:

a light source section including a laser light source;

an optical-path branching device outputting light incident from thelight source section, by branching the light into an outgoing opticalpath of illumination light and other optical path;

a photodetector receiving a light flux that travels on the other opticalpath;

a control section controlling an emitted light quantity in the laserlight source, based on a quantity of the light flux received by thephotodetector; and

a light-quantity-distribution control device disposed between theoptical-path branching device and the photodetector on the other opticalpath, the light-quantity-distribution control device controlling a lightquantity distribution in the light flux to be incident upon thephotodetector.

(2) The illumination unit according to (1), wherein an optical member isprovided, the optical member controlling polarized components toincrease a polarized component same as a main polarized component in theillumination light relatively, in the light flux traveling on the otheroptical path.

(3) The illumination unit according to (2), wherein

the optical member is a polarizing device disposed between theoptical-path branching device and the photodetector on the other opticalpath, and

the polarizing device selectively allows, of the light flux traveling onthe other optical path, the polarized component same as the mainpolarized component in the illumination light to pass therethrough.

(4) The illumination unit according to (2), wherein

the optical member is a dichroic prism serving as the optical-pathbranching device, and

optical characteristics in the dichroic prism are set to allow each ofan optical reflectance and an optical transmittance in the dichroicprism to be substantially constant without depending on a polarizedcomponent.

(5) The illumination unit according to (4), wherein

the dichroic prism includes a reflection transmission film that defineseach of the optical reflectance and the optical transmittance, and

the optical characteristics are set by the reflection transmission film.

(6) The illumination unit according to (2), wherein

the optical member is a dichroic prism serving as the optical-pathbranching device, and

an optical reflectance and an optical transmittance for each polarizedcomponent in the dichroic prism are each set to allow a temperaturechange rate of a reflected light quantity and a temperature change rateof a transmitted light quantity in the dichroic prism to besubstantially equal to each other.

(7) The illumination unit according to (6), wherein the opticalreflectance and the optical transmittance for each polarized componentare each set to allow an amount of a difference between the temperaturechange rate of the reflected light quantity and the temperature changerate of the transmitted light quantity to be substantially 10% or less.

(8) The illumination unit according to (6) or (7), wherein

the dichroic prism includes a reflection transmission film that defineseach of the optical reflectance and the optical transmittance, and

a ratio between the temperature change rate of the reflected lightquantity and the temperature change rate of the transmitted lightquantity is set by the reflection transmission film.

(9) The illumination unit according to any one of (1) to (8), whereinthe light-quantity-distribution control device is a refractive devicewith positive power.

(10) The illumination unit according to any one of (1) to (8), whereinthe light-quantity-distribution control device is a diffusion devicethat diffuses the light flux traveling on the other optical path, thediffusion device outputting the diffused light flux.

(11) The illumination unit according to any one of (1) to (10), whereinthe control section controls the emitted light quantity in the laserlight source to allow the emitted light quantity to be substantiallyconstant without depending on a temperature change.

(12) The illumination unit according to any one of (1) to (11), whereinthe light source section includes, as the laser light source, threekinds of laser light sources which emit red light, green light, and bluelight.

(13) The illumination unit according to any one of (1) to (12), whereinthe laser light source is a semiconductor laser.

(14) A display including an illumination unit that emits illuminationlight, and a light modulation device that modulates the illuminationlight based on an image signal, the illumination unit including:

a light source section including a laser light source;

an optical-path branching device outputting light incident from thelight source section, by branching the light into an outgoing opticalpath of illumination light and other optical path;

a photodetector receiving a light flux traveling on the other opticalpath;

a control section controlling an emitted light quantity in the laserlight source, based on a quantity of the light flux received by thephotodetector; and

a light-quantity-distribution control device disposed between theoptical-path branching device and the photodetector on the other opticalpath, the light-quantity-distribution control device controlling a lightquantity distribution in the light flux to be incident upon thephotodetector.

(15) The display according to (14), further including a projectionoptical system that projects the illumination light modulated by thelight modulation device onto a projection surface.

(16) The display according to (14) or (15), wherein the light modulationdevice is a liquid crystal device.

The disclosure contains subject matter related to that disclosed inJapanese Priority Patent Application JP 2011-153485 filed in the JapanPatent Office on Jul. 12, 2011, the entire content of which is herebyincorporated by reference.It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An illumination unit, comprising: a light sourcesection; an optical-path branching section configured to output lightincident from the light source section, by branching the light into afirst optical path and a second optical path; a photodetector configuredto receive a light flux that travels on the second optical path; acontrol section configured to control an emitted light quantity in thelight source section based on a quantity of the light flux received bythe photodetector; and a light-quantity-distribution control sectionconfigured to control a light quantity distribution in the light flux tobe incident upon the photodetector.
 2. The illumination unit accordingto claim 1, further comprising: an optical member controls polarizedcomponents to increase a polarized component same as a main polarizedcomponent in the illumination light relatively, in the light fluxtraveling on the second optical path.
 3. The illumination unit accordingto claim 2, wherein the optical member is a polarizing section disposedbetween the optical-path branching section and the photodetector on thesecond optical path, and the polarizing section selectively allows, ofthe light flux traveling on the second optical path, the polarizedcomponent same as the main polarized component in the illumination lightto pass therethrough.
 4. The illumination unit according to claim 2,wherein the optical member is a dichroic prism serving as theoptical-path branching section, and optical characteristics in thedichroic prism are set to allow each of an optical reflectance and anoptical transmittance in the dichroic prism to be substantially constantwithout depending on a polarized component.
 5. The illumination unitaccording to claim 4, wherein the dichroic prism includes a reflectiontransmission film that defines each of the optical reflectance and theoptical transmittance, and the optical characteristics are set by thereflection transmission film.
 6. The illumination unit according toclaim 2, wherein the optical member is a dichroic prism serving as theoptical-path branching section, and an optical reflectance and anoptical transmittance for each polarized component in the dichroic prismare each set to allow a temperature change rate of a reflected lightquantity and a temperature change rate of a transmitted light quantityin the dichroic prism to be substantially equal to each other.
 7. Theillumination unit according to claim 6, wherein the optical reflectanceand the optical transmittance for each polarized component are each setto allow an amount of a difference between the temperature change rateof the reflected light quantity and the temperature change rate of thetransmitted light quantity to be substantially 10% or less.
 8. Theillumination unit according to claim 6, wherein the dichroic prismincludes a reflection transmission film that defines each of the opticalreflectance and the optical transmittance, and a ratio between thetemperature change rate of the reflected light quantity and thetemperature change rate of the transmitted light quantity is set by thereflection transmission film.
 9. The illumination unit according toclaim 1, wherein the light-quantity-distribution control section is arefractive section with positive power.
 10. The illumination unitaccording to claim 1, wherein the light-quantity-distribution controlsection is a diffusion section that diffuses the light flux traveling onthe second optical path, the diffusion section outputting the diffusedlight flux.
 11. The illumination unit according to claim 1, wherein thecontrol section controls the emitted light quantity in the light sourcesection to allow the emitted light quantity to be substantially constantwithout depending on a temperature change.
 12. The illumination unitaccording to claim 1, wherein the light source section includes, as alaser light source, three kinds of laser light sources which emit redlight, green light, and blue light.
 13. The illumination unit accordingto claim 12, wherein the laser light source is a semiconductor laser.14. The illumination unit according to claim 1, wherein the light sourcesection includes a laser light source.
 15. The illumination unitaccording to claim 1, wherein the light-quantity-distribution controlsection is disposed between the optical-path branching section and thephotodetector on the second optical path.
 16. The illumination unitaccording to claim 1, wherein the light source section includes a LEDsource.
 17. A display, comprising: an illumination unit that emitsillumination light; a light modulation unit that modulates theillumination light based on an image signal; and the illumination unitincludes: a light source section, an optical-path branching deviceoutputting light incident from the light source section, by branchingthe light into a first optical path and a second optical path, aphotodetector receiving a light flux traveling on the second opticalpath, a control section controlling an emitted light quantity in thelight source section, based on a quantity of the light flux received bythe photodetector, and a light-quantity-distribution control sectioncontrolling a light quantity distribution in the light flux to beincident upon the photodetector.
 18. The display according to claim 17,further comprising: a projection optical unit that projects theillumination light modulated by the light modulation unit onto aprojection surface.
 19. The display according to claim 17, wherein thelight modulation unit is a liquid crystal device.